1. Field of the Invention
The present invention relates to a wireless access communication system, and more particularly to an apparatus and method for controlling a sleep mode in a wireless access communication system.
2. Description of the Related Art
Typically, conventional cellular networks (e.g., a CDMA (Code Division Multiplex Access network), a GSM (Global System for Mobile communication) network, etc.) have widely utilized a slotted paging scheme to implement a sleep mode. In more detail, if it is determined that a current mode is not an active mode, individual terminals operating in such a conventional cellular network remain in a sleep mode which they consume less power, and occasionally awaken from the sleep mode to check reception of their paging signals. If the paging signal is transmitted to any one of the terminals, a corresponding terminal changes its own mode to an active mode. Otherwise, if no paging signal is transmitted to the terminals, the terminals re-enter the sleep mode.
In this case, a unique paging slot between a base station and one terminal is predetermined, such that each terminal awakens from its sleep mode to check its own paging message reception on its unique paging slot. For example, paging slots of individual terminals of a CDMA system are predetermined and paging groups are predetermined in a GSM system, such that CDMA and GSM terminals must awaken from the sleep mode at intervals of a predetermined time. This predetermined time is a fixed time preset by the CDMA or GSM system, such that it is very convenient for the fixed time to be implemented or managed in the CDMA or GSM system.
However, it is difficult to control a sleep mode using a wireless access communication system (also called a 4G (4th Generation) communication system) currently being researched and developed to support a high-speed communication service. In more detail, in the case of a sleep mode proposed by an IEEE 802.16e communication system which takes into consideration mobility of mobile terminals in an IEEE 802.16a communication system, its sleep interval increases according to an exponent power of 2 of an initial sleep interval, i.e., by a multiple of 2 of a previous sleep interval, such that it is difficult to control the sleep mode in the wireless access communication system. In other words, the IEEE 802.16e communication system controls its sleep interval by increasing the interval according to the exponent power of 2 of the initial sleep interval, such that it is difficult for the IEEE 802.16e communication system to manage individual sleep mode start times, individual sleep intervals, and individual awake times of a plurality of subscriber terminals, resulting in difficulty in controlling the sleep mode using the IEEE 802.16e communication system.
FIG. 1 is a flow chart illustrating a sleep mode control method for use in the IEEE 802.16e communication system. Typically, the sleep mode of the IEEE 802.16e communication system begins its operation upon receipt of either a request of a subscriber terminal or a control signal of a base station. A method for beginning the sleep mode control operation using the subscriber terminal's request will hereinafter be described with reference to FIG. 1.
Referring to FIG. 1, a subscriber terminal 10 requesting entry into the sleep mode transmits a sleep request message (i.e., an SLP-REQ message) to a base station 20 at step S31. In this case, the subscriber terminal transmits a minimum size value (e.g., a min-window value) and a maximum size value (e.g., a max-window value) of a desired sleep interval, and a listening interval value serving as a time interval during which a corresponding terminal awakens from the sleep mode to check its own paging message reception. The minimum size value, the maximum size value, and the listening interval value each have a frame unit.
The base station 20 receiving the SLP-REQ message performs a sleep time scheduling operation with reference to predetermined sleep control data (e.g., an allowable min-window value, an allowable max-window value, and an allowable listening interval value, etc.) at step S32, and transmits a sleep response (SLP-RSP) message to the subscriber terminal 10 at step S33. In this case, until the subscriber terminal 10 enters the sleep mode, the base station 20 transmits a variety of messages to the subscriber terminal 10, for example, a specific message (i.e., a start-time value) indicative of the number of remaining frames, a min-window value, a max-window value, and a listening interval value approved by the base station 20. The specific message, the min-window value, the max-window value, and the listening interval value each have a frame unit.
The subscriber terminal 10 receiving the SLP-RSP message enters the sleep mode at a start time contained in the SLP-RSP message at step S34. The subscriber terminal 10 awakens from the sleep mode after the lapse of a sleep interval, and determines whether there is packet data unit (PDU) data to be transferred from the base station 20 to the subscriber terminal 10. In more detail, after the lapse of the sleep interval, the subscriber terminal 10 enters an awake mode at step S35, and checks a TRF-IND message (i.e., a TRaFfic-INDication message called a paging message) broadcast by the base station 20 during the listening interval at step S36. The TRF-IND message is specific information broadcast from the base station 20 to the subscriber terminal 10, and includes basic CIDs (connection IDs) of terminals that the PDU data has to be transmitted to.
The subscriber terminal 10 determines whether its own basic CID (BCID) is contained in the TRF-IND message in such a way that it determines its awake mode. In more detail, if a TRF-IND message received in the subscriber terminal 10 contains a BCID of the subscriber terminal 10, the subscriber terminal 10 recognizes the presence of PDU data to be transmitted to the subscriber terminal 10, such that it awakens from the sleep mode. If the TRF-IND message received in the subscriber terminal 10 is a positive traffic indication message at step S37, the subscriber terminal 10's current status is transitioned to the active mode S38.
If it is determined that a TRF-IND message received in the subscriber terminal 10 does not contain a BCID of the subscriber terminal 10, the subscriber terminal 10 determines that there is no PDU data to be transferred to the subscriber terminal 10, and re-enters the sleep mode. In more detail, if the TRF-IND message received in the subscriber terminal 10 is a negative traffic indication message, the subscriber terminal 10 changes its current mode back to the sleep mode at step S34, and waits for the subscriber terminal 10 to awaken from the sleep mode during the sleep interval.
In this case, the subscriber terminal 10 increases the sleep interval by two times a previous sleep interval at step S39, and maintains the sleep mode during the increased sleep interval at step S34. The subscriber terminal 10 may repeats the sleep mode and the awake mode until entering the active mode. The subscriber terminal 10 increases the sleep interval by two times the previous sleep interval at each repetition time of the sleep and awake modes, and continues to increase the sleep interval until the base station 20 reaches an allowable max-window value of the subscriber terminal 10. As stated above, the IEEE 802.16e communication system increases a sleep interval by two times of a previous sleep interval using a sleep update algorithm, and at the same time begins the sleep mode. Therefore, the IEEE 802.16e communication system increases the sleep interval according to the exponent power of 2 of the initial sleep interval, such that it is difficult for the base station to manage individual sleep intervals of a plurality of subscriber terminals at one time.
In the meantime, three messages are prescribed between the subscriber terminal and the base station to allow the subscriber terminal to enter the sleep mode in the IEEE 802.16e communication system. In more detail, the above three messages are an SLP-REQ message (SleeP REQuest message), an SLP-RSP message (SleeP ReSPonse message), and a TRF-IND message (TraFfic INDication message).
FIGS. 2a to 2d depict exemplary message formats communicating between the base station and the subscriber terminal to control the sleep mode. FIG. 2a is an exemplary format of a sleep request message format 40, and FIG. 2b is an exemplary format of a sleep response message 50a at a sleep denial time. FIG. 2c is an exemplary format of a sleep response message 50b at a sleep approval time, and FIG. 2d is an exemplary format of a TRF-IND message 60.
Referring to FIG. 2a, the SLP-REQ message 40 includes a management message type 41 composed of 8 bits, a min-window value 42 composed of 6 bits, a max-window value 43 composed of 10 bits, and a listening interval value 44 composed of 8 bits. The SLP-REQ message 40 is a dedicated message transferred on the basis of a connection ID (CID) of a subscriber terminal, and is a predetermined message requested when the subscriber terminal desires to enter the sleep mode.
In this case, the management message type field 41 is adapted to indicate the category of a current transmission message. If the management message type is a predetermined value of “45”, this means that a corresponding message is equal to the SLP-REQ message. The management message type 41 is implemented with 8 bits.
The min-window value 42 indicates a requested start value for the sleep interval measured in frame units. The max-window value 43 indicates a requested stop value for the sleep interval measured in frame units. In more detail, the sleep interval is increased by two times the min-window value 42 in the range from the min-window value 42 to the max-window value 43 in such a way that it is updated with a new sleep interval. The listening interval 44 indicates a requested listening interval measured in frame units.
In this case, the min-window value 42, the max-window value 43, and the listening interval 44 are set up in frame units.
Referring to FIG. 2b, the SLP-RSP message 50a refusing the sleep request includes a management message type 51a composed of 8 bits, a sleep-approved field 52a composed of 1 bit, and a reserved field 53a composed of 7 bits. The SLP-RSP message 50a is a dedicated message transferred on the basis of a CID of a subscriber terminal, and is adapted to determine a sleep timing point of the subscriber terminal after the base station finishes scheduling the sleep time of the subscriber terminal.
In this case, the management message type field 51a is adapted to indicate the category of a current transmission message. If the management message type field 51a is set to a predetermined value of “46”, this means that a corresponding message is the SLP-RSP message.
The sleep-approved field 52a is represented in the form of 1 bit. If the sleep-approved field 52a is set to “0”, this means a sleep-mode request denied status. The reserved field 53a is a spare field.
Referring to FIG. 2c, if the base station approves the sleep mode request, the SLP-RSP message 50b includes a management message type field 51b composed of 8 bits, a sleep-approved field 52b composed of 1 bit, a start-time field 53b composed of 7 bits, a min-window field 54b of 6 bits, a max-window field 55b of 10 bits, and a listening interval field 56b of 8 bits.
In this case, the management message type field 51b is adapted to indicate the category of a current transmission message. If the management message type field 51b is set to a predetermined value of “46”, this means that a corresponding message is the SLP-RSP message.
The sleep-approved field 52b is represented in the form of 1 bit. If the sleep-approved field 52b is set to “1”, this means a sleep-mode request approved status.
The start-time field 53b indicates values of frames provided until the subscriber terminal enters the first sleep interval, and does not include a frame receiving the SLP-RSP message. In more detail, the subscriber terminal is transitioned to the sleep mode after the lapse of a predetermined time during which it passes through a plurality of frames ranging from the following frame next to the frame receiving the SLP-RSP message to frames contained in the start-time field.
The min-window field 54b indicates a start value for the sleep interval measured in frame units, the max-window field 55b indicates a stop value for the sleep interval measured in frame units, and the listening interval field 56b indicates a prescribed value for the listening interval measured in frame units.
Referring to FIG. 2d, the TRF-IND message 60 includes a management message type field 61 composed of 8 bits, a NUM-POSITIVE field 62 composed of 8 bits to indicate the number of positive subscribers, and individual CIDs 63 and 64, each composed of 16 bits, of individual positive subscribers. The TRF-IND message 60 is transmitted according to a broadcasting scheme, differently from the SLP-REQ message and the SLP-RSP message.
The management message type field 61 is adapted to indicate the category of a current transmission message. If the management message type field 61 is set to “47”, this means that a corresponding message is the TRF-IND message.
The NUM-POSITIVE field 62 indicates the number of subscriber terminals to which packet data is to be transmitted. The CIDs 63 and 64 of individual positive subscribers include CID information of a specific number indicative of the number of positive subscribers.
FIG. 3 is an exemplary configuration illustrating a sleep interval update algorithm proposed by the IEEE 802.16e communication system. In FIG. 3, ‘SS’ is an abbreviation of a subscriber terminal, ‘BS’ is an abbreviation of a base station, and an exemplary box composed of ‘SS’ and ‘BS’ indicates a frame.
Referring to FIG. 3, the subscriber terminal SS requests the sleep mode from the base station BS at the n-th frame at step S71. Provided that the base station BS sets a sleep mode start-time point to the (n+3)-th frame, and replies to the sleep mode request at step S72, the subscriber terminal SS repeats the sleep interval and the listening interval. Referring to FIG. 3, the first sleep interval is composed of two frames, but the second sleep interval is composed of four frames (double the two frames) contained in the first sleep interval.
As stated above, the conventional IEEE 802.16e communication system commands individual subscriber terminals to enter the sleep mode at different time points, and individual sleep intervals of the subscriber terminals increase according to the exponent power of 2 of the initial sleep interval. Therefore, the IEEE 802.16e communication system has difficulty in controlling individual sleep interval of individual subscriber terminals in the base station, and also has difficulty in grouping and managing the subscriber terminals.
In addition, the base station and the subscriber terminal transmit or receive min-window and max-window information for the sleep interval setup, resulting in an increased amount of transmission data.